Fertilizer and lime recommendations can be confusing. All the different numbers and suggestions can really make it difficult to understand what your soil and crop needs to perform its best. Let’s simplify things with a few quick tips to understanding your soil sample.
Soil pH is the first thing you need to get right. Although some crops are more tolerant of acidic soils than others, your plot will perform best with a pH of 6.5-7.0. Lime is relatively inexpensive and is the key to successful plots. For perspective a plot with a pH of 5.5 is 100 times more acidic than one at 6.5. Over 50% of fertilizer added to a plot with a 5.5 pH is wasted because it is not able to be used by the plants. One to two tons per acre of ag lime is very common to get your plots where they need to be.
Remember that the 3 numbers on bagged fertilizer (N-P-K) are based off of 100 lbs, not 50. In a 50 lb bag of 13-13-13, there are 6.5 lbs or units each of actual nitrogen, phosphorous, and potassium. If your sample says you need 40 lbs each of N-P-K, you would need 350 lbs per acre of 13-13-13. This would give you 45.5 lbs of N-P-K.
An advanced soil test is needed to get current levels of micro nutrients like copper, iron, zinc, boron, etc. These micros are usually not present in bagged fertilizer. Although they are needed in very small amounts in comparison to the macro’s (N-P-K), it can be worthwhile to do an advanced sample every 3-4 years and keep the micro’s up to date.
As a general rule of thumb, cereal grains, corn, and brassicas are nitrogen lovers. Legumes such as clovers, peas, beans, or alfalfa fix their own nitrogen from the atmosphere and need very little at planting time. For example, once established, clover can be fertilized with a common 0-20-20. At planting time, a low nitrogen blend like 5-20-20 can be used to give the young clover a small dose of nitrogen while it develops a root system and begins to affix its own from the air. On the other end of the spectrum, corn can use 100-200 lbs of nitrogen per acre for maximum yield.
Keep in mind if your soil sample comes back with a pretty acidic reading like 4.5-5.5 that your plot is not a lost cause. A couple of tons of lime to the acre can really change how successful your food plot plantings are. Lime is relatively cheap but is often the most overlooked tool to growing good crops for your wildlife. Continuing to spread fertilizer on highly acidic soils can be counterproductive and frankly somewhat a waste of good money. I would much rather see a guy with pH levels below 6.0 spend some of his food plot budget on lime rather than fertilizer.
The time it takes for the lime to begin to breakdown and start to neutralize the acidity on your soil can be dependent on several factors. One of these is how fine the lime has been screened at the quarry. Lime that is screened through a very fine mesh screen is more of a powder consistency and will begin to breakdown in the soil quicker than a more coarse lime screened through a larger screen. Once you have added lime to a plot according to a soil test, it could be 2-5 years before you need to spread more. The amount of time in between applications can vary with different soil types, rainfall amounts, and other factors. Obviously soils that are very sandy will typically leach lime and other nutrients quicker through the root zone than heavier soils with a higher clay content.
Be sure to contact your local farm supply or co-op to spread your lime for you. If your plots are accessible with larger equipment, they can spread the lime for you very efficiently. Another option is to have the lime delivered and dumped on your property and spread yourself. Lime and fertilizer spreaders can often be rented from your local co-op or extension service very reasonably if you have a means of loading it yourself.
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Fertilizer and lime recommendations can be confusing. All the different numbers and suggestions can really make it difficult to understand what your soil and crop needs to perform its best. Let’s simplify things with a few quick tips to understanding your soil sample.
